As a method for reversible fluidization and non-fluidization of a material via application of light, a method in which ultraviolet light and visible light are applied to a liquid crystalline azobenzene compound having a sugar alcohol skeleton (see Patent Literature 1) is known (Patent Literature 2 and Non Patent Literatures 1 and 2). Such reversible fluidization and non-fluidization is realized because the azobenzene structure has photo-reactivity, leading to photo-induced phase transition. FIG. 1 shows photographs showing the conditions of fluidization and non-fluidization of a compound by such method. As shown in FIG. 1, the azobenzene compound in a powdery solid state (the left photograph) is irradiated with ultraviolet light, the compound is liquefied to form a spherical drop (the middle photograph), the drop is irradiated with visible light, a solid that retains a spherical form even if lifted with a spoon is formed as shown in the photograph (the right photograph), the solid is irradiated with ultraviolet light again, and the solid then resumes the form of a spherical drop (the middle photograph).
For application in such method for non-fluidization and fluidization of a compound, an adhesive agent capable of reversible adhesion and peeling with the application of light has been proposed. When a conventional adhesive agent was used, it was difficult to detach the adhered objects from each other without a thermal or mechanical impact, and it was also difficult to use or adhere the detached objects again. Such problems can be overcome with the use of a material that is capable of repeating reversible adhesion and peeling with the application of light. In addition, an azobenzene compound in the form of a polymer comprising an azobenzene structure in its side chain is known to remain capable of reversible fluidization and non-fluidization with the application of light, as with the case of the low-molecular-weight azobenzene compound described in, for example, Patent Literature 1 and gain an increased adhesion force at the time of adhesion (Patent Literature 3).